Natural gas or gases associated to oil productions produced from geological reservoirs, or refinery acid gases often contain(s) acid contaminants, such as carbon dioxide and/or hydrogen sulfide and/or other sulfur compounds, such as mercaptans, COS, CS2, S . . . . For most of the applications of these gas streams, the acid contaminants need to be removed, either partially or almost completely, depending on the application and the type of contaminant.
Methods to remove carbon dioxide and/or hydrogen sulfide and/or other sulfur compounds from a hydrocarbon stream are known in the prior art.
One common approach to remove acid contaminants involves the use of solvents such as chemical solvent (amine-based solvent), hybrid solvent or physical solvent. These solvents have been largely disclosed in the art. However, if appreciable levels of sulfur compounds are present in the acid gas, the most common process to eliminate hydrogen sulfide is to convert said hydrogen sulfide into a non-hazardous product such as elemental sulfur, by sending it to a sulfur recovery unit (“SRU”).
The Claus process is a known type of sulfur recovery process allowing the conversion of hydrogen sulfide into elemental sulfur. In a first step of said Claus process, the hydrogen sulfide is partially burned with air in a Claus furnace to form sulfur dioxide that will react, in a second step, with hydrogen sulfide to form elemental sulfur according to the following reactions:2H2S+3O2→2SO2+2H2O  (1)2H2S+SO2⇄3S+2H2O  (2)
In some embodiments, remaining H2S traces are captured in a Tail Gas Treatment Unit (TGTU), positioned at the outlet of the Claus unit to increase significantly sulfur recovery.
At the outlet of the TGTU, native CO2 is diluted by a large amount of nitrogen coming from the air used for Claus combustion. To recover a purified CO2 stream, CO2 capture technologies using solvent (for example an amine based solvent, such as methylethanolamine (MEA) can be used. However, since the CO2 is diluted in a large volume of nitrogen, the amine based CO2 capture unit requires large size equipments, thereby impacting both CAPEX and OPEX.
Furthermore, an incinerator is generally connected at the outlet of the amine based CO2 capture unit in order to incinerate continuously the remaining traces of sulfur compounds, hydrogen, carbon monoxide and hydrocarbons. It leads to significant fuel gas consumption and to important gaseous CO2 emissions, which constitutes a major drawback of such methods known in the art.
Therefore, there is a need for a method that allows recovering native CO2 from a hydrocarbon feed gas stream which contains acidic compounds, such as CO2, H2S and other sulfur compounds, with better yields, lower investments, lower CO2-emissions and reduced energy consumption compared with the processes of the prior art.
The present invention meets all these needs by providing a method wherein:                A purified CO2 stream comprising at least 90% of CO2 may be recovered,        An oxygen-rich stream is used as a combustive agent for the Claus unit, thereby reducing the size and cost of the equipments,        Hydrogen may be efficiently separated from the CO2 stream and recovered,        An incinerator which works continuously is not required, thereby reducing the energy consumption of the system and the carbon dioxide emission in the atmosphere,        Part of the CO2 stream may be recycled into the Claus furnace to cool it down and facilitate the oxygen-rich operations;        
Unless otherwise indicated, all percentages mentioned in the present patent application are expressed as molar percentages.